Glaciers

Geologists define a glacier as any large mass of ice that moves slowly over land. There are two types of glaciers: Continental glaciers Valley glaciers

Continental Glaciers A continental glacier is a glacier that covers much of a continent or large island. They can spread out over millions of square kilometers. Today, continental glaciers cover about 10% of Earth’s land. They cover Antarctica and most of Greenland.

Continental Glaciers continued Continental glaciers can flow in all directions, spreading out much as pancake batter spreads out in a frying pan. Many times in the past, continental glaciers have covered larger parts of Earth’s surface.

Ice Ages These times in the past when continental glaciers covered large parts of Earth’s surface were known as ice ages. In the past 2 million years, there have been many major ice ages. The most recent ice age ended only about 10,500 years ago.

Valley Glaciers A valley glacier is a long, narrow glacier that forms when snow and ice build up high in a mountain valley. The sides of mountains keep these glaciers from spreading out in all directions. Instead, they usually move down valleys that have already been cut out by rivers. Valley glaciers are much smaller than continental glaciers, but can still be tens of kilometers long.

Formation of Valley Glaciers High in mountain valleys, snow builds up year after year. The weight of more and more snow compacts the snow at the bottom into ice. Glaciers can form only in an area where more snow falls than melts. Once the depth of snow and ice reaches more than 30 to 40 meters, gravity begins to pull the glacier down hill.

Be The Teacher Teach your neighbor what is a glacier. Teach your neighbor the difference between continental glacier and valley glacier.

Formation of Glaciers

Glacial Erosion. The movement of a glacier changes the land beneath it. Although glaciers work slowly, they are a major force of erosion. The two processes by which glaciers erode the land are plucking and abrasion.

Plucking As a glacier flows over the land, it picks up rocks in a process called plucking. Beneath a glacier, the weight of the ice can break rocks apart. These rock fragments freeze to the bottom of the glacier. When the glacier moves, it carries the rocks with it.

Abrasion Many rocks remain on the bottom of the glacier, and the glacier drags them across the land. This process, called abrasion, gouges and scratches the bedrock. You can see the results of erosion by glaciers below.

Be The Teacher Teach your neighbor the difference between plucking and abrasion. Be specific and describe each one.

Glacial Deposition A glacier gathers a huge amount of rock and soil as it erodes the land in its path. When a glacier melts, it deposits the sediment it eroded from the land, creating various landforms. These landforms remain for thousands of years after the glacier has melted. The mixture of sediments that a glacier deposits directly on the surface is called till.

Till Till is made up of particles of many different sizes. Clay, silt, sand, gravel, and boulders can all be found in till. The till deposited at the edges of a glacier forms a ridge called a moraine.

Moraines A terminal moraine is the ridge of till at the farthest point reached by a glacier. Long Island in New York is a terminal moraine from the continental glaciers of the last ice age.

Kettle Retreating glaciers also create features called kettles. A kettle is a small depression that forms when a chunk of ice is left in glacial till. When the ice melts, the kettle remains. The continental glacier of the last ice age left behind many kettles. Kettles often fill with water, forming small ponds or lakes called kettle lakes. Such lakes are common in areas such as Minnesota, that were covered with ice.

Glacial Landforms Fiord: forms when the level of the sea rises, filling a valley once cut by a glacier. Horn: when glaciers carve away the sides of a mountain, the result is a horn, a sharpened peak Cirque: is a bowl-shaped hollow eroded by a glacier. Arête: a sharp ridge separating two cirques. Glacial Lake: Glaciers may leave behind large lakes in long basins. Moraine: forms where a glacier deposits mounds or ridges of till. Kettle Lake: forms when a depression left in till by melting ice fills with water. U-Shaped Valley: A flowing glacier scoops out a U-shaped valley Drumlin: a long mound of till that is smoothed in the direction of the glacier’s flow.

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Check up What kinds of landforms can glaciers make by erosion? Deposition landforms? Explain how a kettle lake forms.